(1) Field of the Invention
This invention relates to the field of building construction or improvement. More particularly, the invention disclosed herein is essentially a device for assuring that the nut remains tight against the cap-plate, as the structural frame shortens. Although the invention has several embodiments, it essentially is a system for rotating a nut on the threaded tip of an anchored rod to maintain tight contact between the nut and the cap-plate (or a washer abutting a surface anchored by the rod).
(2) Background of Invention
There are many situations requiring application of rotational torque upon a fastener, to maintain the tightness of the fastening long after the initial fastening. One example of such a situation involves the need to tighten a nut fastening two structural elements together after one or both structural elements have shrunken from dehydration. For example, lumber used for construction materials typically contains higher moisture when the structure is first constructed, compared to the moisture content after the structure has been constructed for a period of time. This is especially true when the lumber has been newly treated with preservatives and chemicals to withstand moisture. The internal moisture content of the wood construction elements decreases with the passage of time. This process, along with the compression caused by the weight of the structure bearing down on the wood units, eventually results in the shrinkage of the wood units (sometimes called “settling”). The process is most active during the first couple of years, and can result in a 5-6% decrease in the dimensions of wood units; then the process continues for several more years at a slower rate. As a result, many wooden units attached to each other lose their tight connections, thereby potentially creating a danger during the occurrence of catastrophic events such as hurricanes, tornadoes, strong wind and storms, or earthquakes. Maintenance of the tight connections will reduce or prevent damage caused by the repetitive shaking of the structures during the aforementioned catastrophic events contact between the nut and the cap-plate (or a washer abutting a surface anchored by the rod).
The invention is essentially a device to maintain tension between the nut and plate (or washer) on a structural frame when the preservative-treated lumber dries and shrinks over time. Typical construction methods include anchoring the frame of a structure to the foundation of the structure. One such method includes a rod, anchored to the foundation and extending through the lower horizontal base plate of the wall and upward through the uppermost wooden cap-plate and terminating in a nut tightened atop the cap-plate. As the structural frame dries over time (and after the roof is added), shortening of the wall joists often results in a gap of at least a few inches between the cap-plate and the once-tight nut. Such gaps enable high winds to vibrate or move the structure on its foundation, often increasing the gap until the structure can be destroyed or greatly damaged by movement by the wind.
A wide variety of tie-down or take-up systems have been developed to assure that the structural elements remain tightly connected. Known in the art are the following patents and published applications, arguably related to the patentability of the present invention:
U.S. Pat. /App. Pub. No.1st Named InventorDate of Patent/Publication3,806,992Reimer Apr. 30, 19744,721,306ShewchukJan. 26, 19885,364,214FazekasNov. 15, 19945,522,688Reh Jun. 4, 19965,540,530Fazekas Jul. 30, 19967,037,060ComminsMay 2, 20062007/0001451StruvenJan. 4, 20072009/0324364SmithDec. 31, 20097,905,066PryorMar. 15, 20112011/0113711EspinosaJul. 20, 2010
U.S. Pat. Nos. 5,364,214 and 5,540,530 issued to Fazekas disclose a self-adjusting tiedown system having a spring as a retainer, rather than to tighten the nut. These patents disclose a pair of opposing wedges that slide relative to each other, to increase in height to occupy any gap that arises between the nut and the top plate.
U.S. Pat. No. 7,037,060 issued to Commins discloses a shrinkage compensator assembly having an internal compression spring interposed between an innermost base cylinder and an outer sliding cylinder, to urge the sliding cylinder upward to increase the height of the assembly.
U.S. Patent Application Publication No. 2007/0001451 filed by Struven discloses a spring loaded nut for retaining a tubing connection with the tapered end of a vessel fitting. A compression spring within the nut housing biases a ferrule to maintain the tubing in tight engagement with the tapered end of the vessel fitting, to prevent leakage from the vessel through the fitting.
U.S. Patent Application Publication No. 2009/0324364 filed by Smith discloses a self-adjusting shrinkage compensation device having four nut segments around a threaded rod, and coiled spring members flexibly holding the segments against the rod.
None of the above listed references discloses a self-tightening nut assembly, in which the nut automatically rotates around (and down) the threaded tip of a rod to maintain a tightened abutment with whatever the rod is being deployed to hold snug in place. More particularly, none of the above listed references discloses a self-tightening fastener system comprising a wire or line attached to and wound around a nut and attached to a tightening means actuated by a recoil spring.